Nitrate Applications for Hydrogen Sulfide Control

Nitrates are a proven technology for medium to long-duration hydrogen sulfide control in collection system gravity and force mains. They have been used for over 15 years in hydrogen sulfide odor control applications and are a well understood technology. Nitrates can be used in certain applications where hydrogen sulfide odor is already present (curative) or to prevent the formation of hydrogen sulfide (preventative) odor.

Curative Applications

Nitrates react mainly in the water column providing electrons for oxidation. In the curative application mode, a minimum retention time of 2-3 hours is required in order to be effective. In the preventative mode, nitrates condition the biofilm for anoxic process, preventing sulfate from being reduced to hydrogen sulfide in anaerobic sewer conditions.

Preventative Applications

A minimum retention time of 3 hours is necessary in order to be effective. When applied properly, control to low hydrogen sulfide levels is possible. Bioxide may provide some in-line BOD reduction in the collection system. Most calcium and sodium nitrate formulations are considered a non-hazardous material and can be stored in simple feed systems.

Nitrate Properties and Dosing

Nitrate is available as either in either granular or liquid form, and either as a calcium or sodium salt. The granular product comes in 100-lb bags, 2000-lb supersacks, or bulk hopper cars. The liquid product is the more commonly used form, and is available in bulk shipments of 2,000 - 4,000 gallons. Typical calcium nitrate formulations contain 4.3 lbs NO3 per gallon of solution. Typical sodium nitrate formulations contain 3 lbs NO3 per gallon.

Nitrates prevent or remove hydrogen sulfide according to the following equations:

Nitrate Pricing and Sources

The most common form of nitrate on the market for hydrogen sulfide control is liquid calcium nitrate solution. Typical pricing for calcium nitrate solutions is $2.00 to $2.50 per gallon. In the preventative mode, the cost per pound of sulfide treated is anywhere from $4.00 to $20.00. In the curative mode, the cost per pound of sulfide treated is anywhere from $2.00 to $5.00. Nitrates for sulfide control are mostly obtained from fertilizer manufacturers.